Test method for passive device embedded printed circuit board

ABSTRACT

A method of testing a passive device embedded printed circuit board is disclosed. The method in accordance with an embodiment of the present invention includes: applying an AC power to a printed circuit board in which a filter including at least two of a resistor, an inductor and a capacitor is embedded; measuring a property of the filter for the applied AC power; and determining whether or not the printed circuit board is defective by comparing the measured property of the filter with a design value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2010-0019803, filed with the Korean Intellectual Property Office onMar. 5, 2010, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND

1. Technical Field

The present invention is related to a test method for a printed circuitboard in which a passive device is embedded.

2. Description of the Related Art

The conventional passive devices have been mostly mounted on a board byuse of the surface mount technology (SMT). However, as the electronicproducts increasingly become smaller, new packaging technologies forembedding passive devices in the board are actively being developed.

By integrating multiple passive devices in an organic board, the passivedevice embedded board can be manufactured more cost-effectively and isexpected to contribute to making the mobile phones smaller.

However, while there has been an increasing demand for products in whichpassive devices (e.g., capacitor, inductor, resistor, filter, etc.) areembedded in the board using the conventional board technologies andembedded packaging technologies, there have been few test solutions forthe passive device embedded board.

Currently, during the manufacturing and maintenance of the board, theboard needs to be tested due to quality problems, making it imperativeto undertake a step of testing the board in order to secure an adequateproduct quality. Moreover, while the board industry is moving towardmore advanced, integrated, high-functional, reliable and precisiontechnologies, the test equipment for the board needs to be able toprovide a more concrete test and measurement in order to address avariety of problems and secure sufficient board qualities. The boardtest has been used many times for saving the time and cost and improvingthe quality and productivity by testing the performance of the board,solving mounting errors, such as warpage of a device, mis-insertion,reverse-insertion and reverse polarity, and detecting under-soldering,over-soldering and short-circuit.

The purpose of the conventional board test was not to test the passivedevice embedded board but to detect any open/short circuit of lines forthe board. Since the conventional board tester was only able to test theopen/short circuit, it was impossible to test any printed circuit boardhaving a passive device embedded therein.

SUMMARY

The present invention provides a method of testing the performance of aprinted circuit board having a passive device embedded therein.

An aspect of the present invention features a method of testing apassive device embedded printed circuit board is disclosed. The methodin accordance with an embodiment of the present invention can include:applying an AC power to a printed circuit board in which a filterincluding at least two of a resistor, an inductor and a capacitor isembedded; measuring a property of the filter for the applied AC power;and determining whether or not the printed circuit board is defective bycomparing the measured property of the filter with a design value.

The measured property of the filter can be at least one of insertionloss, bandwidth, skirt property, noise level and S-parameter (scatteringparameter).

Additional aspects and advantages of the present invention will be setforth in part in the description which follows, and in part will beobvious from the description, or may be learned by practice of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates different test levels in a method of testing aprinted circuit board in accordance with an embodiment of the presentinvention.

FIG. 2 illustrates a test method of test level 1.

FIG. 3 illustrates a test method of test level 2.

FIG. 4 illustrates a test method of test level 3.

FIG. 5 illustrates a test method of test level 4.

FIG. 6 is a flow diagram illustrating a method of testing a printedcircuit board in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Since there can be a variety of permutations and embodiments of thepresent invention, certain embodiments will be illustrated and describedwith reference to the accompanying drawings. This, however, is by nomeans to restrict the present invention to certain embodiments, andshall be construed as including all permutations, equivalents andsubstitutes covered by the ideas and scope of the present invention.Throughout the description of the present invention, when describing acertain technology is determined to evade the point of the presentinvention, the pertinent detailed description will be omitted.

Hereinafter, some embodiments of a method of testing an electro deviceembedded printed circuit board will be described in detail withreference to the accompanying drawings. Identical or correspondingelements will be given the same reference numerals, regardless of thefigure number, and any redundant description of the identical orcorresponding elements will not be repeated.

As the present invention is related to a test method for measuring aprinted circuit board having a passive device embedded therein, theitems for electrical testing for the printed circuit board in which thepassive device is embedded can be classified as shown in [Table 1]below. The test items are divided into 4 levels, from level 1 to level4, depending on the difficulty and type of the technology.

TABLE 1 Test level for passive device embedded printed circuit boardTest Level Test Item Level 1 Open/Short Test on Normal InterconnectsLevel 2 Single R/C/L Passive Components Test Level 3 Series & ParallelL/C/R Passive Components Test Level 4 Combined Series & Parallel L/C/RPassive Components Test

Test level 1 is conducted for Nets (see (a) in FIG. 1) in whichtransmission lines, which exist within a board and transmit electricalsignals and electric power, are not connected to any passive device. Asillustrated in (a) of FIG. 1, the Net to which no passive device isconnected is simply given an electrical interconnection test to checkwhether it is open between two test points existing in the same Net andan isolation test to check whether it is short between two test pointsexisting in different Nets.

Test level 2, which is illustrated in (b) of FIG. 1, is an electricaltest conducted when one passive device is connected to the transmissionline, and measures an electrical property of the connected passivedevice.

Test level 3, which is illustrated in (c) of FIG. 1, is an electricaltest conducted when a plurality of passive devices have a serial orparallel connection, and measures an electrical property of each of theconnected passive devices.

Test level 4, which is illustrated in (d) of FIG. 1, measures theproperty of the whole circuit when a plurality of passive devices areconnected in series and in parallel.

In an actual passive device embedded printed circuit board, thearrangement of the passive devices existing in the printed circuit boardand the connection structure of the transmission lines can be classifiedas shown in (a) to (d) of FIG. 1. Hereinafter, each test level will bedescribed in detail.

1. Test Level 1

For networks constituted by transmission lines only and not connected toany passive device, as shown in FIG. 2, the electrical test is focusedon whether the networks of conductive lines are properly structuredaccording to the design. Therefore, as shown in (b) of FIG. 2, a currentand a voltage generated as a result of applying a constant current and aconstant voltage between test points connected by a same Net aremeasured, and whether the network is open is checked by measuringresistance. Likewise, resistance is measured in the same way betweentest points constituted by another Net to check whether the network isshort.

For example, as shown in (a) of FIG. 2, test point 1 (TP1) and testpoint 2 (TP2) exist in Net1 and Net2, respectively. In this case, ifresistance measured between TP1 and TP2 is below a reference resistancevalue, it can be inferred that Net1 and Net2 are in the state of short,that is, Net1 and Net2 are not, unlike the design, electricallyseparated. Moreover, as shown in (b) of FIG. 2, both test point 3 (TP3)and test point 4 (TP4) exist in Net3. In this case, if resistancemeasured between TP3 and TP4 is above the reference resistance value, itcan be determined that Net3 and Net4 are in the state of open, that is,Net3 and Net4 are not electrically connected. Some of the common testequipment include the Multi Tester, which can measure the voltage andthe current, and the Source Meter, which is integrated in a power sourceand thus can measure the resistance directly.

In the meantime, it is possible to additionally conduct a low-level testand a high-current test for detecting micro-open, which is one of thereasons causing a progressive defect of a printed circuit board, andmicro-short, which causes noise in an RF system.

2. Test Level 2

As shown in FIG. 3, when one passive device is connected to atransmission line, the electrical test is focused on verification of theelectrical properties of the passive device and the interconnection ofthe transmission line. However, if there is a problem with theinterconnection of the transmission line, the measured properties of thepassive device are greatly affected, and thus testing theinterconnection of the transmission line can be substituted by testingthe electrical properties of the passive device only.

The properties of the passive device can be tested in various waysdepending on the type of the passive device, and the range of electricsignals used for the testing shall be changed according to the capacityof the passive device. In the case of a resistor, a constant voltage anda constant current can be used to detect a voltage and a current, andthe resistance value can be measured, like the method used in test level1. However, in the case of a capacitor and an inductor, an AC power,which changes the size and direction of its voltage and current withtime and has a frequency component, needs to be used in order to measurethe capacitance (C) and inductance (L) up to a low capacity value.

In test level 2, as shown in FIG. 3, by applying an AC signal having aproper frequency and size to a test point to which a passive device isconnected, the size and phase of the voltage and current generated inthe circuit are measured. Through this, an impedance value of thecircuit in which the passive device is included can be measured, and theresistance, capacitance and inductance can be calculated from themeasured the impedance value by using an equivalent model of thecircuit.

Common equipment for measuring the resistor, capacitor, inductor andimpedance of the circuit includes the LCR Meter and the ImpedanceAnalyzer, and the range of measurable resistance, capacitance andinductance may be limited according to the range of measurable voltageand current as well as the range of available frequency.

Generally, low-level capacitance and inductance can be detected when themeasurement frequency is higher, but parasitic components on a circuit,which had little effect on the measurement and thus were ignorable in alow frequency, are gradually increased in a higher frequency, causingerror in the result of measurement.

3. Test Level 3

As shown in FIG. 4, when a plurality of passive devices are bundledtogether in series or in parallel, the electrical test is focused onverification of the electrical properties of each passive device andverification of the electrical integrity of transmission linesconnecting the passive devices. As in the case of test level 2, themeasured properties of the passive device are greatly affected if thereis any problem in the interconnection of the transmission line, and thustesting the interconnection of the transmission line can be substitutedby testing the electrical properties of the passive device.

Like test level 2, test level 3 uses an AC power, which changes the sizeand direction of its voltage and current with time and has a frequencycomponent. However, since at least 2 passive devices are connected intest level 3, the impedance value measured through test points installedon both ends of the circuit is a result of aggregating the impedanceproperties of all of the connected passive devices. Measuring the totalimpedance is not sufficient to guarantee the performance of each passivedevice because the electrical properties of the embedded devices havetolerance. In addition, it would be possible to measure each passivedevice by use of a guarding circuit.

Therefore, test level 3 suggests that whether each passive device isgood or bad is determined by measuring the total impedance and phase inat least two specific frequencies. The frequency can be selected byrunning a simulation program or performing a calculation where theproperties of each passive device are well represented. A moredefinitive analysis would be possible if any continuous change inimpedance and phase according to the frequency is measured.

Common equipment for measuring the impedance and phase of a targetcircuit according to the frequency includes Impedance Analyzer andNetwork Analyzer, and the measurement can be more precise when the rangeof measurable frequencies is wider. It is preferable that the measuringequipment is changed to high frequency equipment as the measurementfrequency becomes higher.

It is preferable that a probe tip used to make an electrical connectionat the test points of the printed circuit board and the transmissionlines for transferring electrical signals to the measurement equipmentare usable in the high-frequency range. It is also possible that thetest points of the board, in which the passive devices are embedded, arepredesigned and placed on the printed circuit board so that a commonprobe tip for high frequency can be used to conduct the measurementwithout separately making a high-cost interface for high frequency.

4. Test Level 4

FIG. 5 illustrates how measurement is made when a plurality of passivedevices are provided in series and/or in parallel to function as asignal filter in a system. In this case, the electrical test is focusedon the result of signal processing that is desired to be achievedthrough this circuit, rather than the electrical properties of eachpassive device.

As in the case of test level 2, the measured properties of the circuitare greatly affected if there is any problem in the interconnection ofthe transmission line, and thus testing the interconnection of thetransmission line can be substituted by testing the electricalproperties of the whole circuit.

An item for evaluating the property of the filter can include anS-parameter (scattering parameter) based on a frequency. Commonequipment for specifying the S-parameter includes Network Analyzer. Asshown in FIG. 5, each of test pads 51, 52, 53, 54, which function asports of the filter, is connected to a corresponding measurement port ofNetwork Analyzer. By sharing a frequency signal distribution result ofan input and output for each port, the S-parameter can be measured.

Meanwhile, the printed circuit board, which is the object ofmeasurement, has a design value through a circuit modeling andsimulation. That is, the design value is pre-obtained through themodeling and simulation, and abnormality of the printed circuit board isdetermined by comparing the design value with a measured value.

Here, the electrical properties that each passive device has can not bemeasured. Therefore, it is not possible to determine which passivedevice has a problem. However, if any of the passive devices isdefective, the overall property of the filter also becomes differentfrom the simulation result, and thus can be used to determine theintegrity. In addition to the S-parameter, other factors, such asinsertion loss, bandwidth, skirt property, noise level, etc., can beused to determine whether the device is good or bad.

5. Test Flow of Passive Device Embedded Printed Circuit Board

FIG. 6 shows a test flow, which is preferably conducted in the order oflevel 1→level 2→level 3→level 4. However, it is also possible tointerchange the order because the connection state is not related to thewhole circuit.

Hitherto, some embodiments of the present invention have been described.However, it shall be appreciated by anyone ordinarily skilled in the artto which the present invention pertains that there can be a variety ofpermutations and modifications of the present invention withoutdeparting from the technical ideas and scopes of the present inventionthat are disclosed in the claims appended below.

A large number of embodiments in addition to the above-describedembodiments are present within the claims of the present invention.

1. A method of testing a passive device embedded printed circuit board,the method comprising: applying an AC power to a printed circuit boardin which a filter including at least two of a resistor, an inductor anda capacitor is embedded; measuring a property of the filter for theapplied AC power; and determining whether or not the printed circuitboard is defective by comparing the measured property of the filter witha design value.
 2. The method of claim 1, further comprising: measuringa total impedance by applying an AC power to a transmission line towhich one or more passive devices are connected; and comparing themeasured total impedance with a design value.
 3. The method of claim 1,wherein the measured property of the filter is at least one of insertionloss, bandwidth, skirt property, noise level and S-parameter (scatteringparameter).
 4. The method of claim 1, further comprising testing whetheror not a transmission line to which no passive device is connected isopen or short.
 5. The method of claim 4, further comprising: measuring atotal impedance by applying an AC power to a transmission line to whichone or more passive devices are connected; and comparing the measuredtotal impedance with a design value.